1. Field of the Invention
The present invention relates generally to the field of disc drive storage, and more particularly to magnetic recording media on directly textured glass substrates.
2. Description of the Related Art
Conventional disc drives are used to magnetically record, store and retrieve digital data. Data is recorded to and retrieved from one or more discs that are rotated at more than one thousand revolutions per minute (rpm) by a motor. The data is recorded and retrieved from the discs by an array of vertically aligned read/write head assemblies, which are controllably moved from data track to data track by an actuator assembly.
The three major components making up a conventional hard disc drive are magnetic media, read/write head assemblies and motors. Magnetic media, which is used as a medium to magnetically store digital data, typically includes a layered structure, of which at least one of the layers is made of a magnetic material, such as CoCrPtB, having high coercivity and high remnant moment. The read/write head assemblies typically include a read sensor and a writing coil carried on an air bearing slider attached to an actuator. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. The actuator is used to move the heads from track to track and is of the type usually referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing closely adjacent to the outer diameter of the discs. Motors, which are used to spin the magnetic media at rates of higher than 10,000 revolutions per minute (rpm), typically include brushless direct current (DC) motors. The structure of disc drives is well known.
Magnetic media can be locally magnetized by a read/write head, which creates a highly concentrated magnetic field that alternates direction based upon bits of the information being stored. The highly concentrated localized magnetic field produced by the read/write head magnetizes the grains of the magnetic media at that location, provided the magnetic field is greater than the coercivity of the magnetic media. The grains retain a remnant magnetization after the magnetic field is removed, which points in the same direction of the magnetic field. A read/write head that produces an electrical response to a magnetic signal can then read the magnetization of the magnetic media.
Magnetic media structures are typically made to include a series of thin films deposited on top of aluminum substrates, ceramic substrates or glass substrates. FIG. 1A illustrates a conventional magnetic media structure built on top of a glass substrate including a glass substrate 110, a nickel-phosphorous (NiP) layer 115, a seed layer 120, a magnetic layer 125 and a protective layer 130. The glass substrate 110 is typically a high quality glass having few defects such as those produced by OHARA Disk (M) SDN. BHD of Melaka, Malaysia. The nickel-phosphorous (NiP) layer 115 is an amorphous layer that is usually electrolessly plated or sputtered onto the glass substrate 110. The NiP layer is used to enhance both the mechanical performance and magnetic properties of the disk. The NiP layer enhances the mechanical properties of the disk by providing a hard surface on which to texture. The magnetic properties are enhanced by providing a textured surface which improves the magnetic properties including the orientation ratio (OR) as is further discussed below. However, the disadvantage of applying the NiP layer 115 is that it adds another step in the process of making magnetic media, which adds to the cost of the magnetic media.
Seed layer 120 is typically a thin film made of chromium that is deposited onto the NiP layer 115 and forms the foundation for structures that are deposited on top of it. Magnetic layer 125, which is deposited on top of seed layer 120, typically include a stack of several magnetic and non-magnetic layers. The magnetic layers are typically made out of magnetic alloys containing cobalt (Co), platinum (Pt) and chromium (Cr), whereas the non-magnetic layers are typically made out of metallic non-magnetic materials. Finally, protective overcoat 130 is a thin film typically made of carbon and hydrogen, which is deposited on top of the magnetic layers 125 using conventional thin film deposition techniques.
FIG. 1B is a flow chart illustrating the prior art conventional method of making the conventional magnetic media structure discussed with reference to FIG. 1A above. First in step 140 a substrate 110 is prepared for deposition prior to cleaning. Next in step 145 the substrate is cleaned using conventional cleaning procedures that clean the substrate and prepares it for thin film deposition. In step 150, the NiP layer 115 is deposited onto the substrate. Typically, the NiP layer 115 is plated onto the substrate, if the substrate is aluminum and sputtered on if the substrate is glass or ceramic. Next in step 155 the NiP layer 115 is mechanically textured. Next in step 160 the seed layer 120 is deposited using conventional thin film deposition techniques. In step 165 the magnetic layer or layers 125 are deposited using similar techniques as used in step 160 to deposit seed layer 120. In step 170, the protective overcoat layer 130 is deposited over the magnetic layers 125. Typically, this protective overcoat layer 130 consists of carbon with hydrogen and is deposited directly after of the previous layer while the substrate remains under vacuum. The protective overcoat layer 130 is typically deposited by transferring the substrate with thin films, while being kept under vacuum, to an adjacent chamber that is isolated from the chambers previously used to deposit films. Protective overcoat layer 130 is typically deposited in an isolated chamber because reactive gasses containing hydrogen or nitrogen can be used in the deposition process. Finally in step 175 the vacuum deposition process ends by moving the conventional media structure into a load lock and unloading the media structure from the vacuum chamber.
Generally, macroscopic in-plane magnetic anisotropy is induced when magnetic recording media are sputtered on mechanically textured NiP coated disk substrates. In such case, the remnant moment (Mrt) is higher in the circumferential direction than in the radial direction. The orientation ratio ORMRT is defined as the ratio of the measured Mrt in the circumferential direction to the measured Mrt in the radial direction. Media with ORMRT>1 is called oriented media and media with ORMRT=1 is called isotropic media. The notation for orientation ratio ORMRT will be abbreviated as OR throughout this disclosure. One way of achieving orientated media on glass substrates 110, is to mechanically texture the NiP layer 115 before films are sputtered onto them as was discussed with reference to FIG. 1B above However, this procedure of depositing a NiP layer 115 onto the glass substrate 110 and mechanically texturing the NiP layer 115 significantly increases the cost of making magnetic media. Magnetic recording media sputtered directly on glass substrates are usually isotropic (ORMRT=1).
The advantages of oriented media is that they have higher thermal stability and better recording performance such as narrow pulse width and low media noise compared to isotropic media. However, the disadvantages of making oriented media on glass substrates are the additional cost and processing which is associated with depositing the NiP layer 115 and consequently texturing the NiP layer.
There exists a particular need for a magnetic recording media comprising an alternate substrate, such as glass or ceramic, which exhibits ORMRT>1 and is suitable for high aerial density recording application. The conventional ways of achieving oriented media on glass substrates are limited to using either mechanically texture NiP pre-coated glass substrates or sputtering NiP on directly textured glass substrates before the deposition of magnetic layers. Therefore what is needed is an alternative system and method that produces oriented media (OR>1) on glass substrates that is as good, if not better, than the conventional means that use a NiP layer. This alternative media will reduce the cost of making high quality media on glass substrates by providing alternative means of making oriented media on glass that does not require the use of NiP and the associated steps that go along with using a NiP layer.